External links to similar and supplementary information:

Extensive data about chemical elements (chemistry, mechanical and thermal properties,
nuclear magnetic moments, etc. etc.) can be found at: http://www.webelements.com

Information about isotopes: http://ie.lbl.gov/education/isotopes.htm

Atomic weights and isotopic composition: http://physics.nist.gov/PhysRefData/Compositions/

xray absorption and other optical data for 30 eV to 30 keV: http://www-cxro.lbl.gov/optical_constants/

A fantastic resource by the author of Mathematica: Wooden periodic table table